1. Field of the Invention
This invention relates to a method and device for controlling the cooling of internal combustion engines in order to reduce corrosive wear of cylinder barrels and piston rings.
2. Description of the Prior Art
The wear of cylinder liners and piston rings in a Diesel engine in most cases is corrosive wear. This applies particularly to engines with high mean pressure. The corrosion substantially is caused by the sulphur content in the fuel. In a Diesel engine in fuel always is combusted at relatively high air excess, which implies that the formation of sulphur trioxide exceeds the formation of sulphur dioxide. Together with the water vapour in the flue gases, the stronger sulphuric acid is formed in addition to sulphurous acid. Due to the combination of corrosion and mechanical wear, the life of the cylinder liners and piston rings is much too short and, thus, constitutes a significant economic problem.
When instead of heavy oil, Diesel oil was used, which has a lower sulphur content, the wear generally was reduced. For various reasons, however, the sulphur content in Diesel oil has been increased lately and thereby the advantages of Diesel oil over heavy oil have decreased. It was found by known experiments, that the corrosion of steel in flue gas with a SO.sub.3 -content of 0.01 and 0.02% has a very distinctive maximum at about 150.degree. C., but that on both sides of the maximum minima are found. Temperatures immediately above 170.degree. C. to 180.degree. C., for example, and immediately below 110.degree. C. to 120.degree. C. are favourable from a corrosion point of view. These temperatures vary slightly with the analysis of the steel and the SO.sub.3 -content of the flue gas, but generally it can be said, that the temperature range between 120.degree. C. and 170.degree. C. of a cylinder liner or piston ring is definitely unfavourable from the corrosion aspect. The temperature of the cylinder liner or, more correctly, the surface temperature on the inside of the cylinder liner, in modern Diesel engines usually is 170.degree.-180.degree. C. when the engine operates at full power output. The temperature, thus, is within a range, at which the corrosion is relatively low and close to minimum. Corrosion problems arise when the engine operates at partial load of its maximum output. Owing to the cooling of cylinder liners and piston rings, their temperature decreases into the corrosive temperature range. Diesel engines or internal combustion engines generally are cooled by a coolant circulated through various passageways and spaces in the engine. The coolant passes outside the engine through a radiator, which is cooled in suitable manner. The cooling unit possibly may be a water intake from a larger water source, for example, sea water or the like. A shunt duct provided for controlling the coolant passageways of the engine is returned by suitably adjusting a three-way valve. The ingoing coolant to the engine, thus, is a mixture of coolant coming from the radiator and return coolant from the engine shunted through the three-way valve.